Santa Clara, Calif. Aimed at portable applications, National Semiconductor Corp. rolled out what it claims is the smallest 2.5-watt, Class D audio amplifier in the world.
In addition, the company introduced a high-output power stereo Class D amplifier. Both Boomer devices, which are filterless, provide high-quality output power with a minimal number of external components for cell phones, smart phones and portable audio devices such as DVD players and gaming devices, said Mike Polacek, vice president of National Semiconductor's Audio group.
The LM4673 mono Class D amplifier comes in a tiny, 0.4 mm-pitch micro SMD package (1.4 x 1.4 mm), and the stereo LM4674 Class D amplifier also provides board-space efficiency for stereo applications in a 2 x 2 mm, 0-5-mm pitch package, Polacek said.
The LM4673 is a fully differential, single-supply, 2.5-watt Class D switching audio amplifier. Consuming less power than any similar Class D audio amplifier available today, the LM4673 has a typical quiescent current of 2.1 milliamps at a 3.6 volts, Polacek said.
The LM4674 is a 2.4-W stereo Class D audio power amplifier. The chip also has a typical quiescent current of 4 mA at a 3.6 V supply for power savings.
National's LM4673 and LM4674 audio amplifiers employ a low-noise, filterless pulse-width modulation (PWM) architecture that eliminates output filters, Polacek said. The flexible power supply requirements of these parts allow operation from 2.4 V to 5.5 V.
Both of these Class D amplifiers have high efficiency with speaker loads compared to typical Class AB amplifiers, Polacek said. Each product features low-power shutdown mode, and advanced pop and click circuitry that eliminates output transients. The gain of the LM4673 is externally configurable to allow the user to connect different multiple inputs while optimizing the gain for each source.
Operating on a single 5-V supply, the LM4673 is capable of driving a 4-ohm speaker load at a continuous average output of 2.5 W with less than one percent total harmonic distortion plus noise (THD+N). In addition, the LM4673 offers a power supply rejection radio (PSRR) of 78 dB at 217 Hz, a common-mode rejection ratio (CMRR) of 70 dB, and a signal-to-noise ratio (SNR) of 97 dB. It also has a typical fast turn-on time of 17 microseconds.
The LM4674 delivers 2.4 W per channel of continuous output power to a 4-ohm load with 10 percent THD+N. The chip features independent left and right shutdown controls to maximize power savings in mixed mono and stereo applications. To give designers flexibility, the LM4674 has four gain settings of 6 dB, 12 dB, 18 dB and 24 dB. The chip also has a PSRR of 75 db at 217 Hz.
See related block diagram
The LM4673 is priced at 90 cents in a lead-free, 9-bump 0.4-mm pitch micro SMD package. The LM4674 is offered in a standard or lead-free, 16-bump micro SMD package and is priced at $1.50. Both are available now and pricing is in 1,000-piece quantities. Click here for the LM4673 data sheet. Click here for the LM4674 data sheet.
National Semiconductor, 1-800-272-9959, www.National.com.